The present invention is generally related to a control system for effective regulation of a power shifted transmission. The invention is in the area of power shifted transmissions such as that described and claimed in U.S. Pat. No. 4,259,882, entitled "Electronic Shift Control", issued Apr. 7, 1981 and assigned to the assignee of this application.
When internal combustion engines began to be utilized in off-road equipment, sliding gear transmissions and manually operated clutches were utilized to match the engine operating speed to the appropriate vehicle speed. Since vehicles of this type have an extremely large rolling resistance and come to a stop in a fraction of a second after the power is removed, the operator had to select a gear for a particular portion of the cycle and start the vehicle by slipping the clutch. When a higher gear was selected, the clutch had to be slipped excessively to get the vehicle moving, resulting in a severely abbreviated clutch life.
As the effort to increase machinery productivity pushed engine horsepower upward and cycle time downward, net types of power transmissions were developed. Torque converters were introduced to automatically provide a portion of the torque multiplication required. Constant mesh gear transmissions with the power path selected manually by engagement of proper jaw couplings were also introduced. Because of shifting difficulties with the mechanical jaw clutches, they were replaced by multiplate, hydraulically actuated disc clutches. Transmissions of this type are in wide use today.
Even with the significant advance in this art illustrated in the patent identified above, there is still a need to further improve shift quality and still maintain the extremely short shift time, that is, the time interval during which power flow through the vehicle drive line is interrupted by the shifting sequence. It is therefore a principal consideration of this invention to provide an improvement in the shift quality even beyond that attained with the system of the above-referenced patent.
Another important consideration is to obtain such shift improvement in part by increasing the system gain, but without causing instability in the system. Another important consideration is to provide an improved control system in which undue loads are not imposed on the range shift clutches after the significant improvement in the main clutches, or forward/reverse clutch, has been achieved.